1. Field of the Invention
The present invention relates to a control device for use on a camera and capable of preventing red-eye effect which tends to be caused in a flash-assisted color photography.
2. Related Background Art
The red-eye effect is a phenomenon in which human eyes are red- or gold-colored in a flash-assisted color photography. This phenomenon is attributable to a fact that the flash light from an electronic flash is applied to and reflected by the retinas through the pupils of human eyes to reach the photographic film. As is well known, numerous capillary blood vessels exist around the retinas to circulate blood containing hemoglobin which is red, so that the image formed by the light reflected from the retinas inevitably becomes red.
Experience shows that the red-eye effect is remarkable particularly under the following conditions:
1) When the photographing environment is dark
The size of the pupil of the human eye varies depending on the brightness of the environment. For instance, the pupil is expanded to about 7 to 8 mm in diameter in the dark. In such a case, the quantity of the light incident to the eye and the quantity of the light reflected by the retina are increased, with the result that the red-eye effect is enhanced correspondingly.
2) When the distance between the light-emitting portion of the electronic flash and the photographing optical axis is small
The retina of a human eye generally has a high reflection factor and exhibits a high directivity of the reflected light. Therefore, the red-eye effect is enhanced when the three elements, i.e., the light-emitting portion, photographing lens and the eye, are located in relation to one another such that the light reflected from the retina can easily come into the photographing lens, i.e., when the light-emitting portion of the electronic flash is located close to the optical axis of the photographing lens. More particularly, the red-eye effect is produced without fail when the angle formed between a line interconnecting the eye of a person as the photographing object and the photographing lens and a line interconnecting the eye and the light-emitting portion of the electronic flash is smaller than a predetermined angle. Experience shows that this angle generally ranges between about 2 and 2.5 degrees. Thus, the red-eye effect would be avoided if the light-emitting portion of the electronic flash is spaced apart from the optical axis of the photographing lens. The distance, however, is practically limited because of the restriction in the distance between the camera and the object (this distance will be referred to as "object distance" hereinafter). Thus, the red-eye effect may be unavoidable under the circumstance in which the object distance is greater than a certain value.
Under these circumstances, methods have been proposed for avoiding the undesirable red-eye effect. For instance, "psa JOURNAL", July, 1952 discloses a method in which the person to be photographed is kept in a bright condition in advance of the photographing so that the state of the eyes is changed to cope with the brightness, and the flash lights up when the pupil diameter has come down below 3 mm, whereby the red-eye effect can be suppressed.
On the other hand, Japanese Patent Publication No. 58-48088 discloses an art in which pre-light-emission is conducted before the photographing over a period necessary for the pupil to reduce its diameter and, when the pupil diameter has been minimized, the flashing section of the electronic flash operates to enable photographing.
Japanese Patent Publication No. 58-9130 discloses an art in which a pair of flash discharge tubes are used such that pre-light-emission is effected by one of these two tubes so as to reduce the pupil diameter and then main-flash is generated by the other tube to enable the photography.
These known methods, however, suffer from various disadvantages as follows.
A first disadvantage is as follows. When pre-light-emission is effected for the purpose of preventing red-eye effect, shutter release with main flash is delayed over a period necessary for the pupil to contract, typically 0.75 second. Therefore, in a camera which is designed to effect the pre-light-emission, the pre-light-emission is wastefully effected even in photography under a bright condition and even in the case where the pupil has contracted as in the case of the second and the following shots in continuous flash-assisted photography in the darkness. In consequence, the photographer may lose the best photo opportunity. In addition, power of the batteries used for the pre-light-emission is wastefully consumed.
A second disadvantage is that, when the power supply or batteries have not been charged sufficiently both for the pre-light-emission and main flashing, there is a risk for the photographer to lose a photo opportunity because of shortage of the electric charge as a result of the discharge for the pre-light-emission.
A third disadvantage is that the pre-light-emission is effective only when the person to be photographed correctly looks at the camera, because the light generated by the pre-light-emission cannot enter the eyes if the eyes do not sight in the direction of the camera. In addition, the person to be photographed tends to mis-understand that the photography is finished upon completion of the pre-light-emission so that he may turn his head or close his eyes when photographed, with the result that the intended shot fails.
A fourth problem is caused by the fact that the intensity of the light generated in the pre-light-emission is constant regardless of the object distance, so that the quantity of light received by the eyes varies depending on the object distance. A too small object distance may cause the face to be unnaturally changed or the eyes to be closed due to dazzle. Such an excessively large quantity of pre-light-emission light received by the eyes is nothing but a wasteful use of the battery power.
A fifth problem is that there are some persons whose pupils do not sufficiently contract by a single pre-light-emission, so that the red-eye effect cannot be suppressed satisfactorily because the known method conducts pre-light-emission only once in advance of the shot.
A camera is known in which, as disclosed in the specification of the U.S. Pat. No. 4,305,647, an electronic flash is activated for pre-light-emission in advance of the shutter release which is accompanied by the main flashing, and the light reflected from the object is measured. The measured value representing the object brightness is used as data for determining the aperture value or as data for judging whether the pre-set aperture value is adequate, with an alarm activated when the aperture value is judged as being inadequate.
When the pre-light-emission for preventing red-eye effect is applied to this type of camera, pre-light-emission is conducted twice: namely, once for determination of the aperture value and once for preventing the red-eye effect. In consequence, battery power is consumed rapidly and the person to be photographed is confused by the repetition of flashing.
A camera also is known which is capable of conducting a timer-assisted photography. In this type of camera, the timer starts to measure the time in response to full pressing of a release button and releases the shutter when a predetermined set time has passed. In most cases, the timer-assisted photographing mode is used when the photographing object is a person or persons. This means that the red-eye effect tends to be experienced frequently in the timer-assisted photography.
The camera having the timer function, when incorporating a flash for preventing red-eye effect, requires that the photographing mode be switched to select the pre-light-emission mode by, for example, pressing a push button, when the timer-assisted photography is to be conducted. Such a switching operation is troublesome and the red-eye effect tends to be caused when the switching has failed.